A promiscuous chloroplast DNA fragment is transcribed in plant mitochondria but the encoded RNA is not edited

Abstract

The RNA editing processes in chloroplasts and mitochondria of higher plants show several similarities which are suggestive of common components and/or biochemical steps between the two plant organelles. The existence of various promiscuous DNA fragments of chloroplast origin in plant mitochondrial genomes allowed us to test the possibility that chloroplast sequences are also edited in mitochondria. AnrpoB fragment transferred from chloroplasts to mitochondria in rice was chosen as it contains several editing sites, two of which match sequence motifs surrounding even non-homologous editing sites in both chloroplast and mitochondrial transcripts. Rice chloroplast and mitochondrialrpoB DNA and cDNA sequences were selectively amplified and the editing status of the cDNA sequences was determined. Three of the four potentialrpoB editing sites previously detected in maize were found to be edited in the rice chloroplastrpoB transcript, whereas the fourth was found to remain unedited. In mitochondria, however, all four editing sites remain unmodified at the cDNA level. This indicates that the editing processes of higher plant mitochondria and chloroplasts are not identical and that organelle-specific factors are required for eliciting the respective editing events.

Hans Kössel passed away on 24 December 1995. We lost an outstanding scientist and a good friend.